A conventional valve device with a valve member for opening and closing the flow path, operated, for example, by manually turning a handle, requires keeping the position of the valve member unmoved so that the open/closed state of the valve remains constant, in order to make constant the flow rate of fluid passing through the valve. In order to make the flow rate constant at various operation states including the state where the flow rate is zero, the valve device is equipped with a lock device.
The lock device disclosed in patent document 1 is one conventional lock device.
The lock device disclosed in patent document 1 is “a lock device for locking a vertical position of a handle of a manually operated fluid flow controller, the lock device being in the shape of an upside-down turned “L” when it is viewed from the side thereof, comprising a handle-holding part having a hole for receiving a root of the handle; and a fixing part for fixing the lock device to a bottom part of the bonnet of the controller, wherein the fixing part extends downward from a base of the handle-holding part at an angle generally perpendicular to the handle-holding part (see claim 1 of patent document 1).” In short, the lock device disclosed in patent document 1 is a member separate from the valve device and it is in the shape of an upside-down turned “L” when it is viewed from the side thereof. Thus the lock device has to be properly kept in a predetermined place so that it will not be lost. Besides, the handle-holding part of the lock device disclosed in patent document 1 is fixed to the root of the handle by, for example, bolting, which makes the fitting troublesome.
The opening and closing lever device for valves disclosed in patent document 2 is another example of the conventional lock device.
The lever device disclosed in patent document 2 includes “a lever 5 with a locking lever 10 and a plate 9 with locking recesses 9b in the rim thereof, wherein a locking hook 10a engages with either of the recesses 9b when the valve is fully open or completely closed, so that the engagement prevents rotation of the lever 5 and excludes the probability of unintended opening/closing of the valve that may be caused by contact with some objects (see lines 5-11 in the upper right column on page 5 of patent document 2).”
The mechanism of preventing rotation of the lever 5 disclosed in patent document 2, however, will not be able to prevent rotation of the valve stem 4 if the mechanism is applied to a valve device whose valve stem 4 is raised and rotationally moved by a change of the pressure of the fluid.